How to get there

Turn off your system after fully saving, and then load to get back to the game.

Go back to the guards. They'll welcome you to the Safari Zone. Tell them No.

Walk out. The game thinks you are still in the Safari Zone.

Walk/ride your bicycle/surf in any route that doesn't have buildings in it (the glitch city is different depending on what route you are in) until you hear the PA's 'Ding-Dong' that will ring after you walk the amount of steps needed. You'll then be teleported to the Safari Zone, where the guards will tell you to come back next time.

Exit the room (door at the opposite side of the room) and you'll find yourself in Glitch City! If you did it on a route with a building in it, you will end up coming out of that building instead.

How to leave Glitch City

To escape, the player needs a Pokémon that knows Fly or Teleport. Use the respective move to go somewhere else.

However, if the player saved the game without a Pokémon that knows Fly or Teleport, they will be stuck in Glitch City.